TimeSys's 14th podcast episode, now available, debunks common misconceptions about real-time Linux. Developers Gene Sally and Maciej Halasz discuss real-time terminology, explain what is and isn't real time, examine the differences between “hard” and “soft” real-time, and explore the major contributors to latency issues.

In the current episode, the pair concentrates on real time concepts and terminology — including interrupts, interrupt service routines, schedulers, priority inheritance, and priority inversion — and how they relate to the capabilities of the Linux kernel.

Although the pair's primary goal in this episode was to establish definitions, they actually succeed at offering pragmatic design guidance that helps our understanding of latency and “realtimeness.”

In particular, they crack the myth that real time means fast or high throughput. “Real time means predictable,” says Sally. Halasz notes that many developers get it wrong because they relate latency to a non-existent guarantee of timing (in Linux kernel terms).

Both engineers agree that Linux is only capable of “soft real-time,” but they assert that most applications do not require “hard real-time” solutions. They also note that powerful soft real-time systems can be architected around the latest kernels, and they promise to explore new kernel friendliness to interrupt issues in a future podcast.

They proceed to dissect three areas — interrupt latency, interrupt handler latency, and scheduler latency — and then begin to explore the concepts of priority inheritance and inversion. They run out of time before exhausting the planned agenda, promising to start where they left off at the next podcast in the biweekly series.

The lively, informal, but savvy and enlightened conversation between Sally and Halasz is available for download in two formats:

• MP3 download

• OGG download

Visit the TimeSys podcast page to download earlier podcasts in the series, or to subscribe to RSS feeds that will inform you of new podcasts as they are published.

Future podcasts will continue the real time discussion.

 
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